The present invention relates to a zoom lens device which is adapted for macro functions, and in particular to a zoom lens device for inexpensive zoom lens cameras which is also adapted for macro photography.
Conventionally, a camera, in particular a compact camera, is typically capable of taking clear picture shots only when the object is at least approximately one meter away. Some of the cameras are equipped with a macro mode which allows a clear picture to be taken even when the object is as close as 60 cm away. However, the pictures which can be obtained by these cameras are often unsatisfactory because the surrounding objects which are located in front and behind the central objects cannot be properly focused. In particular, when the object has a three-dimensional shape, and has a depth, it is not possible to achieve a favorable focusing over the entire object. Furthermore, it has not been possible with the exception of certain specialized cameras to take a clear picture of an object which is at an extremely close range, for instance in the distance range of 10 to 30 cm.
In U.S. Pat. No. 5,960,217 issued to T. Goto on Dec. 28, 1999, the inventor previously proposed a compact camera which can take clear pictures of objects not only in normal distance ranges but also of objects in extremely close ranges. The contents of this prior patent are incorporated in this application by reference.
The zoom lens function used to be available only in high grade cameras, but has since been introduced into less expensive compact cameras in an increasing number. It is widely appreciated that the zoom lens function provides a great photographic versatility to the camera. A zoom lens mechanism typically includes a front lens group and a rear lens group which are placed along an optical center line, and are required to be moved at a prescribed positional relationship so as to vary the composite focal distance while maintaining a proper focusing at the same time.
Combining the macro function with the zoom lens function can even more enhance the versatility of the camera, and expands the photographic freedom of the camera. However, the camera gets highly complex even with the macro lens function alone, and adding the macro lens capability to the camera significantly adds to the complexity of the camera. For this reason, hitherto, it has not been possible to combine both a macro function and a zoom lens function in a compact camera.
Also, it is desired that the camera remains to be easy to use when these functions are incorporated in the camera.
In view of such problems of the prior art, a primary object of the present invention is to provide a zoom lens device which additionally incorporates a macro function with a minimum addition of complexity.
A second object of the present invention is to provide a zoom lens device which additionally incorporates a macro function at a minimum cost.
A third object of the present invention is to provide a zoom lens device which additionally incorporates a macro function without substantially complicating the mode of operation.
A fourth object of the present invention is to provide a a zoom lens device which is suitable for application to inexpensive cameras.
According to the present invention, such objects can be accomplished by providing a zoom lens device, comprising: a device main body; a front lens group supported by the main body so as to be moveable along an optical center line toward and away from the main body; a rear lens group supported by the main body so as to be moveable along the optical center line toward and away from the main body; and an actuating member which actuates the front lens group and the rear lens group at a prescribed positional relationship between a telephoto end and a wide end so as to achieve a variable composite focal length by the lens groups; the actuating member being adapted to place the front lens group and the rear lens groups at positions suitable for a macro lens function when the actuating member is at a point adjacent to the wide end. More specifically, the positions suitable for a macro lens function are defined substantially separately from normal paths for a zoom action of achieving a variable composite focal length so as to permit focusing on an object at an extremely close range which is substantially closer than objects normal for the zoom lens device.
Thus, the mechanism for the zoom lens function can be conveniently used for the macro lens function so that the mechanism for achieving the two functions can be simplified, and the manufacturing cost can be minimized. This zoom lens device can be applied not only to cameras using photographic film but also to digital cameras, video cameras, telescopes and binoculars.
Typically, a front lens retaining member supports the front lens group in an axially slidable and rotationally fast manner while a rear lens retaining member supports the rear lens group in an axially slidable and rotationally fast manner, and the actuating member comprises a rotatable member, typically consisting of a tube disposed, along with the lens retaining members, coaxially with the optical center line, rotatably supported by the main body and engaging the front lens retaining member and the rear lens retaining member via a cam arrangement for converting a rotational movement of the rotatable member into movement of the lens retaining members at the prescribed positional relationship between the telephoto end and the wide end.
According to a preferred embodiment of the present invention, the cam arrangement comprises radial projections formed in the lens retaining members and cam slots formed in the rotatable member engaging the radial projections, and the positions of the front and rear lens groups suitable for a macro lens function are defined by the cam slots.
If the entire stroke of the lens retaining members is desired to be used for the zoom lens function, at least one of the cam slots may define two paths for a corresponding one of the lens groups in a region adjacent to the wide end, the zoom lens device further comprising a member for selectively guiding the lens group into one of the two paths. Thus, this guide member allows selection between the zoom lens function and the macro lens function.
When the actuating member is powered by an electric motor, the device may further comprise a telephoto switch for powering the motor in a direction to actuate the rotatable member toward the telephoto end, a wide switch for powering the motor in a direction to actuate the rotatable member toward the wide end, a macro button for powering the motor into moving the rotatable member into an angular position for holding the lens groups at the position suitable for the macro mode. To avoid inadvertent selection of the macro lens mode, the device may further comprise a motor control circuit for preventing the rotatable member from stopping at the position suitable for the macro mode once the telephoto switch or the wide switch is activated.